Traditional client-server systems employ a two-tiered architecture such as that illustrated in FIG. 1. Applications 102 executed on the client side 100 of the two-tiered architecture are comprised of a monolithic set of program code including a graphical user interface component, presentation logic, business logic and a network interface that enables client 100 to communicate over network 103 with one or more servers 101. A database 104 maintained on server 101 provides non-volatile storage for the data accessed and/or processed by application 102.
As is known in the art, the “business logic” component of the application represents the core of the application, for example, the rules governing the underlying business process (or other functionality) provided by the application. The “presentation logic” describes the specific manner in which the results of the business logic are formatted for display on the user interface. The “database” 104 includes data access logic used by the business logic to store and retrieve data.
The limitations of the two-tiered architecture illustrated in FIG. 1 become apparent when employed within a large enterprise. For example, installing and maintaining up-to-date client-side applications on a large number of different clients is a difficult task, even with the aid of automated administration tools. Moreover, a tight coupling of business logic, presentation logic and the user interface logic makes the client-side code very brittle. Changing the client-side user interface of such applications is extremely hard without breaking the business logic, and vice versa. This problem is aggravated by the fact that, in a dynamic enterprise environment, the business logic may be changed frequently in response to changing business rules. Accordingly, the two-tiered architecture is an inefficient solution for enterprise systems.
In response to limitations associated with the two-tiered client-server architecture, a multi-tiered architecture has been developed, as illustrated in FIG. 2. In the multi-tiered system, presentation logic 221, business logic 222 and database 223 are logically separated from the user interface 220. These layers are moved off of client 225 to one or more dedicated servers on network 203. For example, presentation logic 221, business logic 222, and database 223 may each be maintained on separate servers, 226, 227 and 228, respectively.
This separation of logic components and the user interface provides a more flexible and scalable architecture compared to that provided by the two-tier model. For example, the separation ensures that all clients 225 share a single implementation of business logic 222. If business rules change, changing the current implementation of business logic 222 to a new version may not require updating any client-side program code. In addition, presentation logic 221 may be provided which generates code for a variety of different user interfaces 220, which may be standard browsers such as Internet Explorer® or Netscape Navigator®.
The multi-tiered architecture illustrated in FIG. 2 may be implemented using a variety of different application technologies at each of the layers of the multi-tier architecture, including those based on the Java 2 Enterprise Edition™ (“J2EE”) standard, the Microsoft.NET standard and/or the Advanced Business Application Programming (“ABAP”) standard developed by SAP AG. For example, in a J2EE environment, business layer 230, which handles the core business logic of the application, is comprised of Enterprise Java Bean (“EJB”) components with support for EJB containers. Within a J2EE environment, presentation layer 232 is responsible for generating servlets and Java Server Pages (“JSP”) interpretable by different types of browsers at user interface layer 234.
Although the multi-tiered system illustrated in FIG. 2 provides a more flexible and scalable architecture, it also results in significant additional complexity. For example, debugging an application in business layer 230 may impact the operation of the entire layer. Accordingly, new techniques which simplify the debugging of multi-tiered enterprise systems are desirable.